Preheat the oven to 400 degrees F.
Trim the bottom off the cabbage and cut it in half lengthwise. Then cut it into ½-inch-thick slices.
In a medium bowl, whisk together the olive oil, balsamic vinegar, honey, mustard, garlic powder, onion powder, red pepper flakes, salt and pepper. If possible, it helps to do this in a wide shallow bowl with a flat bottom.
Dip each cabbage slice on both sides in the marinade. Place the slices on a sheet pan in a single layer. They should not be touching or overlapping.
Roast the cabbage for 20-25 minutes until browned in spots and caramelized at the edges.
Sprinkle with parsley before serving.
